This invention relates to hand tools and the like, and more particularly, to a composite hand tool which is made entirely of different types of glass-reinforced plastic material.
Conventionally, wrenches and similar hand tools have been made of iron, steel, or some other metal, because of strength and durability requirements. Metal tools are manufactured using casting or forging procedures. An important disadvantage of metal tools is their cost, both from manufacturing and material standpoints. Moreover, metal tools are unsuitable for use in many applications, particularly when a shock hazard condition exists.
Hand tools have been proposed which include both metal and plastic, the plastic generally forming the handles, or lower-stress receiving portions of the tool. Although this results in reduced cost from a material standpoint, the presence of metal limits use of the tool. Some hand tools have been proposed which are made entirely of a plastic material. However, such hand tools have found limited application because of strength requirements for the work receiving portions of the hand tool. Accordingly, for the most part, the use of plastic in tools has been limited to low-torque wrenches and low-strength pliers, and the like, where high-stress factors are not encountered in use.
Box-end wrenches, both flat and offset, which have been produced by Bonzai, Ltd. of Tokyo, Japan, have a handle formed of unidirectional carbon-fiber epoxy tape with the exterior surfaces covered by a single ply of plain-weave, carbon-fiber epoxy fabric. However, to withstand high local contact stresses, the box end of the flat wrench includes a steel insert which forms the double hex drive configuration for the wrench. The steel hex insert has a plurality of plies of unidirectional tape wrapping the outer diameter of the insert body. The steel insert is attached to the wrench body by a plurality of pins. It was found that using a steel-insert construction results in brittle fiber failure, fiber pullout and matrix delamination during loading. Moreover, the offset box-end wrench yielded less than 40% of the torque strength of its metal equivalent because of low interlaminar shear strength. In addition, the presence of carbon fibers is undesirable because of their inherent conductivity.
In U.S. Pat. No. 5,062,328, there is disclosed an open-ended wrench having a body made of glass-fiber-reinforced plastic material with a gripping head having a polygonal opening in which there is embedded a metal insert of hard steel with a polygonal opening to bear high contact stresses during use of the wrench. The wrench requires a metal insert to withstand the gripping stresses which are exerted at the point of contact between the jaw of the wrench and a nut being turned by the wrench.
There is a need for wrenches and other hand tools which are non-metallic and therefore nonmagnetic, nonconductive and non-sparking, which are made of low cost materials, and which are inexpensive to manufacture, but yet have strength comparable to that of a metal tool of comparable size.